The use of wireless communication links, whether for video, voice, or data, have become prevalent in recent years, particularly in light of the widespread adoption of mobile technology, such as cellular telephones, laptop computers, personal digital assistants (PDAs), pagers, and the like. Wireless communication links are particularly desirable with respect to some situations, such as to avoid obstacles associated with laying cable between communication nodes, providing freedom of movement, etcetera. Accordingly, wireless communication links have been given much consideration by communication infrastructure providers. However, deploying wireless communication links is not without difficulty. In particular, wireless spectrum is often highly regulated and may be prone to interference.
Wireless broadband access has been considered quite extensively in recent years. Although multiple solutions have been experimented with, attempts at providing wireless broadband access, particularly widespread access, has generally not met with commercial success due to inadequate economical conditions, i.e., high cost without sufficient demand. In particular, the need for licensed spectrum in which to provide wireless links has typically resulted in high costs to wireless broadband access providers. Moreover, past wireless broadband access solutions have typically implemented non-standard or application specific equipment, due to each provider developing a unique solution tailored to their particular situation, circumstances, and spectrum, thereby preventing economies of scale and compatibility.
Demand for such wireless broadband access has generally been associated with applications and appears to be correlated to at least some degree to the cost of the service and equipment, the complexity of the implementation, and the reliability of the links. The proliferation of wired broadband access, such as via cable modem and digital subscriber line (DSL), is stimulating the creation of applications requiring relatively large amounts of bandwidth, such as music downloading, video streaming, multi-media presentations, etcetera. However, a large number of nodes and/or locations desirous of implementing such emerging applications are not yet wired for broadband access and, therefore, cannot adequately access such applications.
Two related wireless technologies are beginning to gain acceptance in providing at least some level of wireless broadband access, these being wireless technologies based on the Institute of Electronic and Electrical Engineers (IEEE) 802.11 and 802.16 standards, which are incorporated herein by reference. The 802.11 standard is directed toward indoor applications and sets forth asynchronous protocols for short range communications, while the 802.16 standard is directed toward outdoor applications and sets forth synchronous protocols for longer range communications, each being operable in unlicensed spectrum such as within the 2 to 11 GHz range. Implementation of such standards facilitates equipment cost reduction by providing for compatibility and economy of scale. However, technologies adopting the foregoing standards heretofore have not adequately addressed the issues associated with commercial or economic deployment of wireless broadband access. For example, although addressing aspects such as communication protocols, the standards alone do not provide for spectrum utilization suitable for reliable or large scale wireless broadband access.
Traditional wireless services rely upon licensed spectrum, in which the use of the spectrum is highly regulated such that sources of interference are avoided, in order to provide for spectrum utilization suitable for reliable or large scale access. However, that spectrum is expensive and is very difficult to obtain. Unlicensed bands, although providing an abundant, readily available, and inexpensive alternative, present a challenge in that the spectrum is open to many simultaneous uses and thus prone to unpredictable interference leading to link degradation and even blocking. Such link degradation and blockages are typically not experienced uniformly throughout the wireless links of a communication network, often resulting in a high degree of service level variance experienced by users. That is, although unlicensed spectrum can provide an enormous amount of transmission bandwidth, bandwidth variance resulting from interference presents a significant challenge to the successful use of this spectrum.
Channel planning is a traditional approach that has been used, such as by cellular network providers, to avoid and/or mitigate interference issues. Accordingly, channel planning has been considered for use with respect to multiple operators' use of unlicensed spectrum. Unfortunately, channel planning (at least when used alone) is inadequate for many unlicensed spectrum networks because un-cooperative radio sources are present (i.e., those not abiding by the channel planning scheme). Moreover, channel planning schemes typically contradict channel agility and consequently greatly reduce the ability to avoid interference by changing operating channels.
The typical approach to avoid interference within unlicensed spectrum is to limit the transmission power as defined by FCC part 15 sections 15247 and 15249. In this “brut-force” approach the transmission power is limited to very low level, thereby reducing service coverage and buildings penetration rendering broad band service over unlicensed spectrum almost impractical.
Other prior attempts to address interference have included adjusting data rates based on frame drop rate feedback, such as where a transmitter monitors the rate of dropped frames (e.g., based on ARQ reports). For example, when a dropped frame rate is below certain target value, the transmitter may increase the data rate and visa versa for dropped frame rates that are above this value. A transmitter may use a substantial amount of time to determine the dropped frame rate (e.g., tens of frames for statistically sufficient sample). When multiple subscriber stations (N) are being served, the time for determining the dropped frame rate is increased by factor of N. In addition, re-transmit “timer” values implemented by many ARQ based protocols add to the delay between the frame dropping events and the associated reports. Consequently the transmitter reaction to an increase or decrease in frame drop rate is often relatively slow. The foregoing is aggravated when a subscriber station's link budget is highly variable, such as may result from variable distance and shadowing. In operation according to such prior attempts at providing adjustable data rates, when a channel is clear of interference even subscriber stations that have relatively good reception (signal to noise ratio) are being served with much lower data rate that their link budget allows. Moreover, when a channel is frequently interrupted by interfering signals with a substantial duty cycle, the transmitter is most likely unable to track the frame drop rate changes and the resulting operation will be to adjust the data rate to the minimum possible.
Accordingly, a need exists in the art for systems and methods providing for utilization of spectrum suitable for reliable and/or large scale wireless access. Particularly, a need exists in the art for systems and methods which provide acceptable levels of communication services to all subscribers in light of unpredictable interference associated with the use of unlicensed bands. A further need exists in the art for systems and methods utilizing spectrum prone to interference without implementing channel planning regimes.